System, method and arrangement which can use spectral encoding heterodyne interferometry techniques for imaging

ABSTRACT

Systems, arrangements and methods for obtaining three-dimensional imaging data are provided. For example, a broadband light source can provide a particular radiation. A first electro-magnetic radiation can be focused and diffracted, and then provided to at least one sample to generate a spectrally-encoded line. A second electro-magnetic radiation may be provided to a reference, which may include a double-pass rapidly-scanning optical delay, where the first and second electro-magnetic radiations can be based on the particular radiation. An interference between a third electro-magnetic radiation (associated with the first electro-magnetic radiation) and a fourth electro-magnetic radiation (associated with the second electro-magnetic radiation) can be detected. The spectrally-encoded line may be scanned over the sample in a direction approximately perpendicular to the line. Image data containing three-dimensional information can then be obtained based on the interference. The exemplary imaging methods and systems can be used in a small fiber optic or endoscopic probe.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority fromU.S. patent application Ser. No. 60/686,518, filed May 31, 2005, theentire disclosure of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Development of the present invention was supported in part by the U.S.Government under National Science Foundation grant BES-0086709. Thus,the U.S. Government may have certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates to optical imaging and, more particularly,to systems, methods and arrangements that can use spectral encodingheterodyne interferometry techniques for imaging at least one portion ofa sample.

BACKGROUND OF THE INVENTION

Three-dimensional (“3D”) endoscopy can assist with a variety ofminimally invasive procedures by providing clinicians with depthinformation. Achieving depth-resolved imaging having a large,three-dimensional field of view can be difficult when small diameterflexible imaging probes such as, e.g., borescopes, laparoscopes, andendoscopes are utilized. The use of confocal imaging through afiber-bundle using a high numerical aperture lens may be one techniquethat can be used to address this problem. Such technique is describedin, e.g., Y. S. Sabharwal et al., “Slit-scanning confocal microendoscopefor high-resolution in vivo imaging,” Appl. Opt. 38, 7133 (1999). A 3Dfield of view for such devices, however, may be limited to less than afew millimeters due to a small clear aperture of the objective lens anda low f-number that may be required for high-resolution opticalsectioning.

Other techniques such as, for example, stereo imaging and structuredillumination have also been proposed for obtaining 3D endoscopic images.Such techniques are described in, e.g., M. Chan et al., “Miniaturizedthree-dimensional endoscopic imaging system based on activestereovision,” Appl. Opt. 42, 1888 (2003); and D. Karadaglic et al.,“Confocal endoscope using structured illumination,” Photonics West 2003,Biomedical Optics, 4964-34, respectively. These techniques may, however,require more components to construct a probe than would be required forconfocal imaging that is performed using a fiber bundle. This additionalhardware can increase the size, cost, and complexity of such devices.

Spectrally-encoded endoscopy (“SEE”) techniques can utilize a broadbandlight source and a diffraction grating to spectrally encode reflectanceacross a transverse line within a sample. For example, a two-dimensionalimage can be formed by slowly scanning this spectrally-encoded line.This technique can be performed using a single optical fiber, therebyenabling imaging through a flexible probe having a small diameter. Inparticular, SEE images can have a larger number of resolvable points,and may be relatively free from pixilation artifacts as compared withimages obtained using fiber-bundle endoscopes.

When combined with interferometry techniques and systems, SEE canprovide three-dimensional images. A depth-resolved imaging can beachieved, e.g., by incorporating a SEE probe into a sample arm of aMichelson interferometer. Using such an arrangement, two-dimensional(“2D”) speckle patterns can be recorded using a charge-coupled device(“CCD”) camera at multiple longitudinal locations of a reference mirror.Subsequently, depth information can be extracted by comparinginterference signals obtained at consecutive reference mirror positions.When using this technique, the reference mirror can be held stationaryto within an optical wavelength while a single image (or line) is beingacquired to avoid the loss of fringe visibility. Scanning a referencemirror that is positioned with such accuracy over multiple discretedepths can be very difficult at the high rates required for real-timevolumetric imaging.

OBJECTS AND SUMMARY OF THE INVENTION

One of the objects of the present invention is to overcome certaindeficiencies and shortcomings of the prior art systems (including thosedescribed herein above), and to provide exemplary SEE techniques,systems and arrangements that are capable of generatingthree-dimensional image data associated with a sample. Exemplaryembodiments of the present invention can provide methods, systems andarrangements that are capable of generating high-speed volumetricimaging of a sample. Exemplary embodiments of these systems andarrangements can be provided within the confines of a fiber optic probeor an endoscopic probe.

In certain exemplary embodiments of the present invention, a system canbe provided that includes a light source or another electro-magneticradiation generating arrangement. The light source can be a broadbandsource capable of providing the electro-magnetic radiation. Theexemplary embodiment of the system can include a beam splitterconfigured to separate radiation from the light source into a firstradiation and a second radiation. The system can be configured to directthe first radiation toward a sample. The first radiation can passthrough a lens-grating arrangement (that can include a diffractiongrating and a lens) to focus, modify and/or direct the first radiation.The lens-grating system can be configured to direct a spectrally-encodedline associated with the first radiation towards the sample. A scanningmechanism can also be provided that is configured to effectuate thescanning of the line over at least a portion of the sample in adirection that is approximately perpendicular to the line. A thirdradiation can be generated based on interactions between at least aportion of the spectrally-encoded line and the sample. The lens-gratingarrangement and/or the scanning mechanism may be provided, e.g., in aprobe. The probe may include an endoscope and/or a catheter.

The exemplary embodiment of the system can further include arapidly-scanning optical delay (“RSOD”) arrangement, where the secondradiation can be configured to pass through the RSOD arrangement andpossibly be affected thereby to generate a fourth radiation. A detectionarrangement can also be provided that is configured to detect aninterference between the third and fourth radiations. This detectionarrangement can include, e.g., a charge-coupled device that is capableof generating raw data based on the interference.

A processing arrangement such as, e.g., a computer and/or a softwarearrangement executable by the processing arrangement, can be providedthat is/are configured to generate the image data based on the detectedinterference between the third and fourth radiations. The processingarrangement and/or the software arrangement can be configured to apply,for example, a Fourier transform to the raw data to generate the imagedata. A display arrangement can also be provided to display the imagesof at least one portion of the sample based on the image data. Theseimages can optionally be displayed in real time, e.g., while the firstradiation is being directed towards the sample.

In further exemplary embodiments of the present invention, a method canbe provided for generating three-dimensional image data of at least aportion of the sample. A particular radiation can be provided which mayinclude a first radiation directed to the sample and a second radiationdirected to a reference. For example, the first radiation can bedirected through a lens and a diffraction grating to provide aspectrally-encoded line directed towards the sample. This line can bescanned over at least a portion of the sample in a directionapproximately perpendicular to the line. A third radiation can beproduced based on an interaction between the first radiation and thesample. A fourth radiation can be generated by directing the secondradiation through a rapidly-scanning optical delay.

An interference can then be detected between the third radiation and thefourth radiation. This interference can be used to generatethree-dimensional image data that characterizes at least one portion ofthe sample. The image data can be used to display images of the sampleon a display.

These and other objects, features and advantages of the presentinvention will become apparent upon reading the following detaileddescription of embodiments of the invention, when taken in conjunctionwith the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying figures showing illustrative embodiments of theinvention, in which:

FIG. 1 is a block diagram of an exemplary embodiment of a time-domainspectrally-encoded imaging system according to the present invention;

FIG. 2 is a diagram of an exemplary technique that may be used toextract both transverse and depth information from an interference traceusing a short-time Fourier transform in accordance with certainexemplary embodiments of the present invention;

FIG. 3A shows an exemplary image of a fingertip obtained using a method,system and arrangement in accordance with exemplary embodiments of thepresent invention;

FIG. 3B shows an exemplary image of the fingertip shown in FIG. 3A inwhich depth information is superimposed using contour lines;

FIG. 4A is an image of a surface of a quarter dollar coin obtained usinga method, system and arrangement in accordance with exemplaryembodiments of the present invention;

FIG. 4B is an image of a surface of a dime placed 2.4 mm in front of thequarter dollar coin shown in FIG. 4A;

FIG. 4C is an exemplary two-dimensional integrated image of the twocoins shown in FIGS. 4A and 4B, which was obtained using a method,system and arrangement in accordance with exemplary embodiments of thepresent invention; and

FIG. 4D is a depth-resolved image of the two coins shown in FIG. 4C, inwhich surface features closer to the lens are brighter than thosefurther away; and

FIG. 5 is a flow diagram of an exemplary method in accordance withexemplary embodiments of the present invention.

Throughout the figures, the same reference numerals and characters,unless otherwise stated, are used to denote like features, elements,components or portions of the illustrated embodiments. Moreover, whilethe subject invention will now be described in detail with reference tothe figures, it is done so in connection with the illustrativeembodiments. It is intended that changes and modifications can be madeto the described embodiments without departing from the true scope andspirit of the subject invention as defined by the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF INVENTION

A block diagram of a system configured to acquire image data for 3Dimages in accordance with exemplary embodiments of the present inventionis shown in FIG. 1. For example, a light source 100 or other source ofelectro-magnetic radiation can be provided (which may generate a lightor other electro-magnetic radiation that has a broad bandwidth such as,e.g., a titanium-sapphire laser) which may be coupled to an input portof, e.g., a single-mode fiber optic 50/50 splitter 110 or another typeof optical splitter. A compact lens-grating arrangement may be providedthat can include a lens 120 (e.g., a lens having f=40 mm and a beamdiameter of 0.5 mm) adapted to focus a beam of light, and a transmissiongrating 130 having, e.g., 1000 lines/mm (Holographix LLC) to diffractthe beam and form a spectrally-encoded line (along an x-axis) on asurface of a sample 140. A galvanometric optical scanner 150 can beprovided for, e.g., slow scanning of the line along a y-axis.

This exemplary system can provide a spatial transverse resolution of,e.g., approximately 80 microns. The image may include 80 transverseresolvable points, with each transverse spot capable of beingilluminated using a bandwidth of, e.g., 1.9 nm. The overall powerprovided to the sample may be about 4 mW. A double-pass rapidly-scanningoptical delay (“RSOD”) 160 can be used to control a group delay of thereference arm light. The RSOD 160 may be scanned over a distance ofabout 1.5 mm at a rate of about 1000 scans per second. An interferencesignal can be recorded as a function of time by a detector 170, and thendemodulated and displayed in real time using a computer 180.

Spatial resolutions and ranging depth measurements and visualization canbe improved according to the exemplary embodiments of the presentinvention by using, for example, a broader bandwidth source and anextended-range optical delay line. Such arrangements are described,e.g., in K. K. M. B. D. Silva, A. V. Zvyagin, and D. D. Sampson,“Extended range, rapid scanning optical delay line for biomedicalinterferometric imaging,” Elec. Lett. 35, 1404 (1999).

An illustration of an exemplary technique according to the presentinvention for encoding both transverse and depth dimensions usingbroad-spectrum illumination is shown in FIG. 2. For example, a sample200 can include three discrete scattering points in an x-z plane. Aninterference signal 210 that may be recorded as a function of time byscanning the sample 200 can contain three interference traces 220. Eachinterference trace can represent depth information which may becharacterized by a corresponding delay, Δt_(i)=Δz_(i)/v_(g), whereΔz_(i) is a depth location of a corresponding scatterer and v_(g) is agroup-delay velocity. A transverse location can correspond to a carrierfrequency, 2v_(p)/λ_(i), where v_(p) can represent a phase velocity andλ_(i) may be a wavelength corresponding to the location of scatterer i.(For example, in the sample containing three scatterers shown in FIG. 2,i=1 to 3.)

The width of each trace, T_(i), can determine a depth resolution, andmay be expressed as T_(i)=0.44N_(x)λ_(i) ²/(v_(g)Δλ), where Δλrepresents a total bandwidth and N_(x) is a number of resolvable pointsalong the spectrally-encoded line. A two-dimensional data set 230(corresponding to locations in x- and z-axes) can be obtained byapplying a short-time Fourier transform (“STFT”) to the interferencedata 220 using a Gaussian window centered at Δt_(i) and having a widthof T_(i). The frequency distribution corresponding to a given delayΔt_(i) can provide spatial information at a corresponding depth, Δz_(i).

Alternatively or additionally, a depth-integrated transverse image canbe obtained by applying a frequency transform to part or all of a set ofinterference data simultaneously, or by summing individualdepth-resolved images. The frequency transform may be, e.g., a Fouriertransform, a short-time Fourier transform, or a Wigner transform.Volumetric data can be obtained by scanning the spectrally encoded linetransversely across the sample 200.

The exemplary detection technique according to the present inventiondescribed herein can be analogous to a technique which may be used inconventional optical coherence tomography (“OCT”). Conventional OCTtechniques are described, e.g., in D. Huang et al., Science 254, 1178(1991). Exemplary OCT techniques can utilize a broadband light source toobtain a high resolution in an axial direction which may be, e.g., lessthan about 10 μm. To perform three-dimensional imaging using theconventional OCT techniques, a probe beam should be scanned in twodimensions, which can require a fast beam-scanning mechanism. Incontrast, spectrally-encoded endoscopy techniques can utilize a spectralbandwidth to obtain both transverse and axial resolution simultaneously,which may thereby utilize only one slow-axis scan to acquirethree-dimensional data sets. Using a given source bandwidth, thetwo-dimensional resolution can be achieved with a decreased axialresolution.

If an exemplary shot-noise limited detection technique is utilized and asource having a uniformly flat spectrum is used, a signal-to-noise ratio(“SNR”) associated with a spatial point having a reflectivity R can beexpressed as:

${{SNR} = {\frac{2\frac{P_{r}}{N_{x}}R\frac{P_{s}}{N_{x}}}{2{hvP}_{r}B} = \frac{2{RP}_{s}\tau}{{hvN}_{x}^{2}N_{z}}}},$where P_(r) denotes a total reference arm power, P_(s) denotes a totalsample power, τ represents a line scan period, B denotes a samplingbandwidth, which may be written as B=N_(z)/2τ, and N_(z) indicates anumber of axial resolvable points. The expression for the SNR above canbe inversely proportional to the square of the number of transverseresolvable points, since only a fraction of the reference arm power(i.e., P_(r)/N_(x)) interferes with light returning from a singletransverse location.

Exemplary images of a fingertip acquired using an exemplary 3Dspectrally-encoded technique in accordance with certain exemplaryembodiments of the present invention are shown in FIGS. 3A and 3B. Theframe size of these exemplary images is approximately 15×9 mm).Three-dimensional image data was obtained at a rate of 2.5 frames persecond. Each frame in the images of FIGS. 3A and 3B includes aresolution of 200 points (along a spatially scanned axis)×80 points(along a wavelength-encoded axis)×10 points (indicating depth within thesample). The depth resolution was approximately 145 μm.

For example, a two-dimensional (depth-integrated) image 300 of FIG. 3Acan be obtained by acquiring about 4000 points per scan, and applying aFourier transform to these data. Each scan can be divided into about tentime windows that may be transformed separately to extractthree-dimensional information. The three-dimensional data can also bepresented as a contour map 310 as shown in FIG. 3B. Further, afalse-color image can be generated and superimposed onto atwo-dimensional image to provide an additional three-dimensionalvisualization.

In biological tissues, a single-scattered signal emerging from aparticular depth within a tissue sample can have a significantly lowerintensity than a signal scattered from near the tissue surface. Based onthis characteristic of scattered signals, it is likely that the largestfrequency component of each STFT may correspond to a surface height ordepth within the tissue.

Three-dimensional image data can be obtained from the samples having adepth range larger than, e.g., the 1.5 mm depth provided directly by theRSOD 160 shown in FIG. 1. A greater range of depths can be resolved byobtaining two or more volumetric data sets, where each set can beacquired using a different reference arm path length.

In exemplary embodiments of the present invention, certain components ofthe system may be provided in a small size in the form of a probe thatcan be introduced into a body. For example, the lens-grating arrangementand/or the scanning mechanism may be provided in a capsule or otherenclosure or housing that can be included with or introduced into a bodyusing a catheter and/or an endoscope. A waveguide can be used to directat least part of the radiation generated by the light source to thelens-grating arrangement, the reference, and/or the sample. Thewaveguide can include, for example, a single-mode optical fiber, amulti-mode optical fiber, and/or a multiple-clad optical fiber.

As an example of this extended range acquisition, the surface of a dimeplaced about 2.4 mm in front of a quarter dollar coin was imaged asshown in FIGS. 4A-4D using a method, arrangement and system inaccordance with certain exemplary embodiments of the present invention.For example, a lens having an f value of 65 mm was used to provide alarger field of view and depth of focus. Two volumetric data sets wereobtained by calculating the STFT for each of two locations of the RSODdouble-pass mirror. Each set of image data included 200 horizontallines, captured at a rate of 5 volume sets per second, and was processedand displayed on a computer screen at a rate of 2.5 frames per second.

Images of the two coins shown in FIGS. 4A-4D are provided under variousconditions. A first image 400 in FIG. 4A includes a scale bar having alength of 1 mm, which also corresponds to the images shown in FIGS.4B-4D. Although the surfaces of both imaged coins are within the focaldepth of the lens, the dime is not seen in the first image 400 of FIG.4A because of the limited scanning range of the RSOD. After adjustingthe optical path length of the reference arm by stepping the RSOD 160double pass mirror of FIG. 1 by 2.4 mm, the surface of the dime can bevisualized, as shown in a second image 410 in FIG. 4B.

The two volumetric data sets used to form the first and second images400, 410 can be combined to obtain a depth-integrated two-dimensionalthird image 420 of FIG. 4C and an extended-range depth resolved fourthimage 430 of FIG. 4D. The surface height in the resolved fourth image430 can be represented by a gray scale lookup table, where depthlocations closer to the lens have higher pixel intensity. Thus, theimage of the dime appears brighter, whereas recesses in the lowerquarter dollar coin appear the darkest in this image. Other exemplaryimage processing techniques may be used to provide additional displaysof the three-dimensional image data obtained using the exemplary methodsand systems described herein.

An exemplary flow diagram of a method 500 according to exemplaryembodiments of the present invention is shown in FIG. 5. A particularradiation can be provided that can include a first and a secondelectro-magnetic radiation (step 510). The particular radiation can beprovided by, e.g., a broadband light source or a laser. The radiationcan include a plurality of wavelengths that are provided simultaneously,or it can optionally can include one or more wavelengths that vary intime. The first and second radiations can be provided, e.g., bydirecting the particular radiation through an optical arrangement suchas a beam splitter.

A spectrally disperse line of radiation can be generated that isassociated with the first radiation (step 520). This line can begenerated, e.g., by directing the first radiation through a lens-gratingarrangement which can include, for example, a diffraction grating and alens that can be configured to focus and/or direct the first radiation.The spectrally disperse line can be generated all at once or,alternatively, different portions of the line can be generatedsequentially when using a light source having at least one wavelengththat varies with time.

The spectrally disperse line can be directed toward a portion of asample to be imaged (step 530). The line may also be scanned in adirection that can be approximately perpendicular to the line (step 540)using an arrangement such as, e.g., a galvanometric optical scanner orthe like, which can provide coverage of a region of the sample to beimaged.

The second radiation can be directed to an optical delay arrangement(step 550) or other arrangement such as, e.g., a RSOD, which is capableof affecting the second radiation in a controlled time-dependent manner.A signal associated with the first and second radiations may then bedetected (step 560). This signal can be, e.g., an interference which canbe obtained by combining the second radiation (after it has beendirected to the optical delay arrangement) and electro-magneticradiation generated by an interaction between the first radiation and aportion of the sample being imaged (step 570). Three-dimensional imagedata can then be generated that is associated with the signal using aprocessing arrangement or computer. The data can be generated, e.g., byapplying a Fourier transform to the signal and/or demodulating thesignal. One or more images can then be displayed using the image data(step 580). Optionally, the image can be displayed in real time.

The foregoing merely illustrates the principles of the invention.Various modifications and alterations to the described embodiments willbe apparent to those skilled in the art in view of the teachings herein.Indeed, the arrangements, systems and methods according to the exemplaryembodiments of the present invention can be used with any OCT system,OFDI system, SD-OCT system or other imaging systems, and for examplewith those described in International Patent ApplicationPCT/US2004/029148, filed Sep. 8, 2004, U.S. patent application Ser. No.11/266,779, filed Nov. 2, 2005, and U.S. patent application Ser. No.10/501,276, filed Jul. 9, 2004, the disclosures of which areincorporated by reference herein in their entireties. It will thus beappreciated that those skilled in the art will be able to devisenumerous systems, arrangements and methods which, although notexplicitly shown or described herein, embody the principles of theinvention and are thus within the spirit and scope of the presentinvention. In addition, to the extent that the prior art knowledge hasnot been explicitly incorporated by reference herein above, it isexplicitly being incorporated herein in its entirety. All publicationsreferenced herein above are incorporated herein by reference in theirentireties.

1. A system comprising: at least one first arrangement configured toprovide a particular radiation which includes at least one firstelectro-magnetic radiation directed to at least one sample and at leastone second electro-magnetic radiation directed to a referencearrangement, wherein at least one of the at least one first radiation orthe at least one second radiation comprises a plurality of wavelengths,and wherein the at least one first arrangement is configured tospectrally disperse the at least one first electro-magnetic radiationalong at least one portion of the at least one sample; and at least onesecond arrangement configured to generate data is based on the at leastone second electromagnetic radiation, wherein the data is axial datathat is associated with at least one portion of the at least one samplewhich is located in a direction that is axial with respect to adirection of the at least one first electro-magnetic radiation.
 2. Thesystem according to claim 1, wherein the reference arrangement comprisesan optical delay arrangement.
 3. The system according to claim 2,wherein the optical delay arrangement is a rapidly-scanning opticaldelay.
 4. The system according to claim 1, wherein the data is furtherassociated with at least one portion of the at least one sample which islocated in a direction that is transverse with respect to a direction ofthe at least one first electro-magnetic radiation.
 5. The systemaccording to claim 4, wherein the data is further associated with atleast one of a two-dimensional image or a three-dimensional image of atleast a portion of the at least one sample.
 6. The system according toclaim 1, wherein the at least one sample is an anatomical structure. 7.The system according to claim 6, wherein at least a portion of theanatomical structure is provided below a surface of skin.
 8. The systemaccording to claim 1, wherein the at least one first arrangementcomprises a diffraction grating.
 9. The system according to claim 8,wherein the at least one first arrangement further comprises a lens. 10.The system according to claim 9, wherein the at least one firstarrangement is further configured to generate a line of radiation on atleast a portion of the at least one sample.
 11. The system according toclaim 10, wherein the at least one first arrangement further comprisesat least one scanning arrangement configured to scan the line ofradiation in a direction approximately perpendicular to the line. 12.The system according to claim 1, wherein the at least one secondarrangement comprises an optical detector.
 13. The system according toclaim 12, wherein the optical detector includes a charge-couple device.14. The system according to claim 12, wherein the optical detector isconfigured to generate a signal based on the at least one firstelectromagnetic radiation and the at least one second electromagneticradiation, and wherein the at least one second arrangement is configuredto generate a time-frequency transform of the signal.
 15. The systemaccording to claim 14, wherein the time-frequency transform is at leastone of a short-time Fourier transform, or a Wigner transform.
 16. Thesystem according to claim 1, further comprising a processing arrangementconfigured to provide at least one image based on the data.
 17. Thesystem according to claim 16, wherein the at least one processingarrangement is configured to provide the at least one image in realtime.
 18. The system according to claim 1, wherein the at least onefirst electromagnetic radiation is provided through a waveguidearrangement.
 19. The system according to claim 18, wherein the waveguidearrangement is at least one of a single-mode optical fiber, a multi-modeoptical fiber, or a multiple-clad optical fiber.
 20. The systemaccording to claim 18, wherein the at least one first arrangement isprovided in a probe.
 21. The system according to claim 20, wherein theprobe comprises at least one of an endoscope or a catheter.
 22. A methodfor generating three-dimensional image data comprising: providing aparticular radiation which includes at least one first electro-magneticradiation and at least one second electro-magnetic radiation; directingthe at least one first electro-magnetic radiation to at least onesample, wherein the at least one first radiation comprises at least oneof a plurality of wavelengths and the at least one first electromagneticradiation is spectrally dispersed on the at least one sample; directingthe at least one second electro-magnetic radiation to a referencearrangement; detecting a signal associated with the at least one secondelectro-magnetic radiation; and generating image data associated basedon the signal, wherein the image data is axial data which is furtherassociated with at least one portion of the at least one sample which islocated in a direction that is axial with respect to a direction of theat least one first electro-magnetic radiation.
 23. The method of claim22, wherein the reference arrangement includes an optical delayarrangement.
 24. The method of claim 22, wherein the at least one firstelectromagnetic radiation is provided in the form of a line, and furthercomprising scanning the line in a direction approximately perpendicularto the line.
 25. The method of claim 22, wherein generating the imagedata comprises generating a time-frequency transform of the signal. 26.The method of claim 25, wherein the time-frequency transform is at leastone of a Fourier transform, a short-time Fourier transform, or a Wignertransform.
 27. The method of claim 22, further comprising displaying atleast one image based on the image data.
 28. The method of claim 27,wherein the at least one image is displayed in real time.
 29. The methodaccording to claim 23, wherein the optical delay arrangement is arapidly-scanning optical delay.